1. Field of the Invention
This invention relates to a mechanism for mounting an ink ribbon cassette, in which an ink ribbon for printing is housed.
2. Description of Prior Art
In a printing device such as a typewriter, or the like which performs printing of letters and characters by application of percussive force onto a printing sheet using type elements and an ink ribbon, there has been widely adopted a system, wherein, with a view to enabling the ink ribbon to be replaced with ease and without staining the hands of an operator of the printing device, an ink ribbon cassette (hereinafter simply referred to as a "cassette") housing therein an ink ribbon is placed on a carriage of the printing device.
FIG. 1 of the accompanying drawing illustrates schematically a construction of a printer head section of a typewriter, on which the cassette is mounted.
In the illustration, a reference numeral 1 designates a platen which functions to feed a printing sheet and to serve as a printing table. In front of the platen 1, there is horizontally arranged a supporting shaft 5 along and in parallel with the platen 1. A carriage 2 is mounted on this supporting shaft 5 in a freely slidable manner.
At the rear part of the carriage 2, an endless belt 6 to be driven and run by an electric motor 7 is fixedly secured, with which the carriage 2 is caused to move along the platen 1.
At the front part of the carriage 2, there are mounted a character wheel 4 as the printing means and a hammer 3 to strike any of the character type elements on the wheel 4 at the time of printing. A cassette 8 containing therein an ink ribbon 9 is also fitted on this carriage 2 in a manner to surround the character wheel 4 and the hammer 3.
The cassette 8 contains, in the main body 8" of its casing unit 8', a spool (not shown) with unused ink ribbon 9 wound around it and a take-up spool (not shown) to wind the used ink ribbon 9 on it. The cassette 8 has a pair of arm portions 8a, 8a with their forward ends facing the platen 1 defining an open space. The ink ribbon 9 extended between both spools runs through these open sections of the arm portions 8a, 8a to be exposed outside.
The cassette 8 is mounted on the carriage 2 in such a manner that the ink ribbon 9 extended and running between the forward ends of the arm portions 8a, 8a of the cassette 8 may be positioned with a gap between the character wheel 4 and a printing sheet (not shown in the drawing) on the platen 1. At the time of the printing operations, any character type element on the character wheel 4, which is hit by the printing hammer 3 at its back, applies the percussive force onto the ink ribbon 9 to thereby perform printing of the character or letter on the printing sheet.
On the other hand, the cassette 8 is usually provided with two pivot points (not shown in the drawing) to shift the ink ribbon 9 downwardly so that the operator of the printing device is able to see the printed character or letter at every printing operation. At the time of printing, the cassette 8 is pivoted up and down by a shift mechanism (not shown) with the pivot points as the center of oscillation.
Most of the conventional constructions of the mechanism for mounting the cassette 8 on the carriage 2, as mentioned above, adopt a system wherein an elastic member is provided on one part of the cassette main body 8" so that the cassette 8 may be mounted on the carriage 2 by being pushed against the resilient force of this elastic member and may be removed from the carriage 2 by being pulled out against the resilient force.
In such construction as mentioned above, however, since the direction in which the cassette 8 can be removed from the carriage 2 is restricted when the operator tries erroneously to pull out the cassette 8 forcibly with vigor, the cassette 8 or the mounting mechanism itself may be disadvantageously damaged.
As another structure of the conventional cassette mounting mechanism, there has been mostly adopted a system wherein the above-mentioned two pivot points are used as the operating points for the mounting and dismounting of the cassette 8, the pivot points of which are held in position or released from it by means of a claw-shaped hooking member (not shown). With this construction, however, since the two pivot points must be arrested or released simultaneously at the time of the cassette mounting and dismounting, the mechanism becomes inevitably complicated and the printing device as a whole becomes disadvantageously expensive.